Bending of wood



Feb. 6, 1940. K. MICHAELIS 2,139,073

BENDING OF WOOD Filed Oct. a, 1937 2 Sheets-Sheet 2 PEG INVENTOR.

Patented Feb. 6, 1940 UNITED STATES PATENT OFFICE Application October 8, 1937, Serial No. 168,035

In Germany October 15, 1936 7 Claims.

This invention relates to the bending of wood, and more particularly to novel processes and machinery for dry-bending wood panels and the like.

It is an object of this invention to provide methods and devices for dry bending, i. e. for bending without previous boiling or steaming,

wood panels and the like, including blanks of con-- siderable thickness.

It is another object of this invention to provide 1 I methods and devices whereby t o dry-bend wood panels and the like in a small fraction of the time involved in prior procedures and at correspondingly low expense.

Other objects, and the manner in which they u are attained, will appear from the following description,

In the prior art it has been customary to bend wood by first subjecting it to a thorough boiling or steaming treatment whereby to thoroughly im- 20 pregnate it with moisture, thereafter molding the wet blank, mostly under pressure, and finally drying the bent shape by storing each piece over an extended period of time, frequently not less than 48 hours, in individual molds or clamps. Evident ly, this procedure is time-consuming and requires costly installations, a great number of molds and considerable storage space, apart from the fact that the physical and chemical properties of the wood undergo material changes in consequence '0 of the lixiviation with hot water or steam. In

view of all these disadvantages, there had been frequent attempts at providing methods and apparatus for dry-bending wood, all of which are however,'only applicable in certain specific cases 86 and are moreover limited to comparatively thin stock. The present invention ultilizes in a novel manner the circumstance that dry wood, when heated, is rendered temporarily compressible and in that 40 state can bemolded. According to the invention I first heat uniformly the inner side, i. e. that side which in the bendingoperation becomes the concave side, of substantially the entire panel part to be bent so as to build up in this panel part a 45 temperature gradient with the higher temperaarea of a flat panel part of considerable length and widthas distinguished from heat sources having substantially only a spot or line heating effect-an amount of heat sufficient to render the wood compressibleJ 5 In order to avoid heat losses on the inner side of the panel, to which the heat is applied, I prefer arranging the heat source so closely adjacent to the mold or bendingdevice as to prevent cold air from coming in contact with the inner side of the panel before. and during the bending. To this end, in a preferred embodiment of my invention I arrange the heat source tangentially and close to the curved mold surface and pull the panel away from this heat source in constant sliding contact with it and around and into parallel relation to the curved mold surface, which is preferably heated also.

In order to avoid friction between the wood and the mold and to facilitate the operation, the mold may be supported for rotation by means of a crank, a. weighted lever, a spring under tension,

a motor of some kind or by other means, and, when thus rotated, will wind up the heated panel.

Instead of thus pulling the sheet in order to 26 move it away from the heating device, I may impart to the mold, to which the heated panel is fixed, rolling motion relative to and in contact with the panel, thereby causing the heated side of the panel to apply itself to thefcurved mold 3 surface.

In this way I am enabled to bend large panels of considerable thickness without any appreciable risk of breakage of the outer layers. Curvatures of 100 mms. radius can easily be obtained with 8-10 mm. sheets; thinner sheets can of course be curved through smaller radii. If the panels are properly preheated and if provision is made for feeding to the mold afresh preheated sheet right after the curved panel is removed from the mold, 0 the bending process can becarried through at a quantity production rate.

Having thus explained the principle underlying a my. invention, I will now proceed to describe some means of carrying same out on an industrial scale, having reference to the drawings afllxed to this specification and forming part thereof which illustrate by way of example and in a purely diagrammatic manner some devices embodying my invention and adapted to produce curved shapes by bending panels of plain and plywood.

In the drawings Fig. 1 shows in a purely diagrammatic manner the pulling of a preheated panel onto and around lifted ofi the heater.

a stationary curved mold, represented by way of example by a steel or copper cylinder.

Fig. 2 is a diagram showing a modified way of carrying out the same operation. g

Fig. 3 illustrates in a similar manner the winding up of a preheated panel on the cylindrical surface of a mold arranged for rotation about its axis.

' Fig. 4 illustrates another manner of winding up a preheated panel for the purpose of bending it. 1

Fig. 5 is an elevation of a bending machine embodying the principle of operation illustrated in Fig. 3, and

Fig. 6 is'a similar view of another bending machine embodying the principle of operation lllustratedin Fig. 4, while Fig. 6a illustrates'the machine of Fig. 6, however, with the parts shown in their end positions.

Fig. 7 is a partial end view of the machine, shown in Fig. 6, partly in section, and

Fig. 8 illustrates a detail.

Referring to the drawings and first to Fig. l, l is a support for a mold cylinder 2 arranged for.being heated in any suitable manner, for instance by means of electrical resistance wires or the like 2a. The uprights further support a preheating device, represented in the drawings by an electrical heating plate 3. Rollers 4 extending across the heater 3 and spaced from its surface about the thickness of the panel to be bent serve to prevent the sheet, shown at 5, from being 6 is a gripper which is here shown in a conventional manner as gripping the edge portion of the panel; I is a chain fixed to the gripper and extending around part of the mold and 8 is a spring placed under tension by means of a pedal lever 9 and exerting on the gripper and the panel a pull .suflicing to force it into contact with the hot mold surface as soon as it is heated up to the extent of being prepared for bending. As soon as this stage has been reached, the panel of wood will be pulled around the mold and into contact with its surface and, in trying to follow the descending chain, will be curved at right angles to the horizontal part of the panel, the radius of curvaturebeing determined by the radius of the mold.

The curved portion of the panel will substantially retain its curvature. With panels of a certain thickness a tendency, prevailing only as long as the panel is warm, of expanding again. can be counteracted by mounting the curved panels in suitablecages until they have cooled down, or by bending. them somewhat farther than required.

Instead of pulling the panel by hand or by means of a spring of some sort, it may be carried or wound around the mold cylinder by an arm rotated by a motor. This is shown in a conventional manner in Fig. 2, where 98 is the gripper arm fixed to a gear wheel Ill mounted on the mold axle at H and meshing with a pinion I2 secured on the shaft of an electromotor l3, which drives the wheel l0 and arm 98 and causes the panel to be pulled off the heater plate and around the mold.

While in the two instances mentioned above the mold may be or is stationary, Fig. 3 illus-,..

trates a particularly eilicient manner of bending panels, in which the mold is arranged for rotatign about its axis, thus avoiding all friction between the panel and the mold and using the mold itself as a means for pulling and winding up the preheated Panel.

In Fig. 3 the mold I4 is mounted for rotation about its axis and an arm I5 carrying a weight I I6 is fixed torits axle I1 and at I 8 to the mold cylinder proper. The weight I6 has the tendency to drop under the influence of the gravity force, so as to turn the arm or lever l5 and corre-= spondingly the mold l4 fixed to such arm. l9 represents a resistance heating the mold and 20 is some sort of gripping means fixed to the cirthe mold will be insuificient to overcome the resistance offered by the wood, as long as the panel 2! is cold or not preheated to the extent of being pliable. Only when this point is reached, the lever action of the weight will gradually overcome the resistance of the panel to a change of form and in slowly turning the mold in the direction of the arrow will pull the panel oil the heater and will wind it up on the mold, as shown in dot and dash lines. Owing to the elasticity of the; pull exerted on the sheet, provided that the weight and leverage are adapted to the wood thickness, no undue stress will be exerted on the outer layers of the wood and cracking and splitting, which might arise when forcing the panel onto the mold by a constant force, will be avoided with certainty. I v

This principle of operation is utilized in the bending machine illustrated in Fig. 5, wherein 26 is one of the standards, 25 is the mold cylinder,-

26 is a gear keyed on the mold axle 21, 28 is a larger gear meshing with gear 26 and mounted to turn on an axle 29 in the standards. 30 is the weighted lever arm keyed on the axle 29,31 is an auxiliary arm carrying a counterweight 32 and pivoted to the arm 30 near its pivot point.

v33 is the gripper fixed to the mold cylinder, 34

panel being preheated to'bending temperature,

the action of the weighted lever arm 30 will pull the panel off the heater plate 36 and around the mold as shown in dot anddash lines. Owing to the insertion of a step-up gearing between the arm and the mold an'angular displacement of the arm through an angle of 60 may cause the mold cylinder to rotate through an angle of as is here required in order to bend the panel U-fashi0n.

The winding up of 'the panel of wood on a rotatory curved molding surface can also be effected in the manner illustrated diagrammatically in Fig. 4. Here, instead of shifting the panel relative to the heater and pulling it on the mold rotating in stationary bearings, the heater is shifted relative to the panel, the plane part of which remains stationary, and the mold is arranged to roll relative to and to wind up the preheated part of the panel. By thus arranging the coacting parts I am enabled to wind up and bend both ends of a panel simultaneously, either in the same or in opposite directions. As shown in the diagram of Fig. 4, 4| and 42 are two shap ing cylinders, one placed above, the other below thepanel indicated at ill. 43 and 44 are heating plates arranged in contact with the panel in front of the cylinders 4| and 42, respectively. The heaters are pivoted, by means of. links indicated at 45 and 46, respectively, to the axles 41 and 48, respectively, of their cylinders.

Assuming the panel to be gripped by the two cylinders at the points of contact 49, 50 and the portions of the wood in front of the cylinders to be preheated, the cylinders, if forced to roll relative to and in contact with the sheet, for instance by springs 99 gripping the cylinders, will wind it up and bend it as illustrated in dottedlines, the heaters being shifted relative to the panel as the cylinders go through their rolling movement. This mode of operation is followed in thebending machine shown in Figs. 6-8, in which the two ends of a panel are bent'simultaneously in opposite directions at about right angles to the middle portion of the panel. Weighted levers are again resorted to for supplying the bending force. 5| is the machine structure and 52, 53 are horizontal guideways formed thereon at different levels. 54, 55 are slide pieces forming bearings supporting the axial journals 56 and 51 oftwo semi-cylindrical shaping molds 58 and 59, respectively, which may be heated in any suitable manner. Arms 60, BI, carrying weights 62, are fixed on the mold journals, preferably one on eitherside of each mold. Between the mold ends and the slide pieces are keyed on the mold journals toothed wheels 53, 64 which mesh with racks 65, 66, respectively, secured on the structure 5| (Figs. 7 and 8). Evidently, when the weighted levers drop after the wood has been rendered sufficiently pliable to permit of rotary displacement of the molds, the aforementioned gear arrangement gives rise to a controlled longitudinal displacement of the molds; for example, as shown in Fig. 6, the molds 58 and 59 are caused to move in a. direction toward each other. 51, 58 are the preheating plates carrying arms 69, 19, by means of which they are pivotally secured to the mold journals. The heater 6'! rests on the panel to be bent, while the heater 68 is supported for sliding motion on the structure by means of laterally projecting pins. 95. g

The gripping device for holding the panel down on the mold 59 is shown in Fig.1 '7 as comprising to be bent is fixed to the two molds by means of the gripping devices 12, 11, by inserting the panel between the mold and the presser bar cooperating therewith, and actuatingith'e correlated eccentric so as to force the presser bar onto the panel to clamp the same firmly on the mold, and on the panel being preheated to bending temperature, the weighted levers will overcome its resistance to bending and will begin to move in the direction of the arrows, rotating the molds which, when so rotated, are forced by the toothed wheel and rack gearings to roll relative to the sheet, their axles sliding, with their bearings 54, 55, in the horizontal guideways, in the direction toward each other, so as to reduce the distance between the molds as required by the winding-up operation thereof. In this rolling movement the molds shift their heaters 61, 58 in front of them in contact with the sheet. When the lever arms have swung through 90, the molds have completed a quarter turn and have forced the ends .0f 'the panel to bend around into the position shown in Fig. 6a. By turning the top heater 6'! into vertical position the S-shaped panel can be turned about its transverse middle line and lifted free of the molds, which are then returned into their initial positionr When bending panels on a quantity basis, a number of panels may be arranged on juxtaposed heaters and heated up simultaneously. Evidently, the shifting of panels from one auxiliary preheating device to the adjacent one which is situated more closely to the main heating and bending station, or the shifting of panels to such station, as well as the supply of panels to that auxiliary preheating device which is most remote with respect to such main station, may be carried out manually or by any well known mechanical means. In this manner the rate of ing of a plurality of panels may of course be dispensed with. v

The panels can also be wound up through more than 360 to form double-walled cylinders.

The preheating of the panels, which was described as being done with the aid of plate heaters, might as well be effected by means of hot gases orflexible heaters, as explained more fully in my copending applications for U. S. Patent Serial Nos. 173,574 and 253,111.

While in the examples here given circular and semi-circular shaping molds are used, it is obvious that molds or bending tools of non-circular and, more especially with thinner sheets, also polygonal surface and of irregular surface may be applicable.

In the foregoing specification and the appended'claims, the term dry-bending is intended to refer to the bending of inwardly dry panels, as distinguished from the bending of panels which have been rendered pliable by thorough impregnation with moisture, e. g. b boiling and/or steaming; and the term wood panels is intended to include all kinds of blanks, such as boards, strips and the like, composed of wood fibres, including composite materials of wood and a binder, such as plywood.

Various changes may be made in the details disclosed in the foregoing specification without departing from the invention or sacrificing the advantages thereof. I

I claim: n

1. The process of dry-bending wood panels an the like, which comprises preheating uniformly the inner side of substantially the entire part to be bent of an inwardly dry panel so as to build up therein a temperature gradient with the higher temperature on the inner side of said part whereby to render the wood on said inner side compressible, and immediately thereafter and while the wood on said inner side still retains substantially said temperature, bending the part thus preheated.

2. The process of dry-bending wood panels and the inner side of substantially the entire part to be bent of an inwardly dry panel so as to build up therein a temperature gradient with the.

part thus preheated by forcing said inner side into face to face contact with a hot molding surface.

3. The process of dry-bending wood panels and the like, which comprises preheating uniformly the inner side of substantially the entire part to be bent of an inwardly dry panel so as to build up therein a temperature gradient with the higher temperature on the inner side of said part whereby to render the wood on said inner side compressible, and immediately thereafter and while the wood on said inner side still retains substantially said temperature, bending the part thus preheated by pulling it around a hot molding surface.

4. A device for dry-bending wood panels and the like, comprising in combination, a fiat-surface heater for heatingone surface of part of a panel, a curved mold closely adjoining said heater, and means for bending the heated surface of the panel part into contact with said mold, said surface to become the concave surface of the bent part.

5. A device for dry-bending wood panels and the like, comprising in combination, a-flat-sunface heater for heating one surface of part of a panel, a curved mold closelyadjoining said heater and means for pulling the panel part-sf heated by said heater away .from said heater and around said mold with the heated surface fi becoming the concave surface of the bent part.

6. A device for dry-bending wood panels and 7. A device for dry-bending wood panels and i the like, comprising in combination, a curved mold supported for rotation, a flat-surface heater for heating one surface of part of a panel, said KARL I" 

